The present invention relates in general to a three tool system for manipulsating radioactive fuel rods, and more particularly, to such a system for the extensive on-site remote visual inspection of such radioactive fuel rods which are arranged in an array within a nuclear fuel assembly and located underwater for storage in a spent fuel pool.
In water-cooled nuclear reactors, a plurality of elongated fuel rods and control rod guide thimbles are arranged, as a closely spaced array, in a unified structure known as a nuclear fuel assembly. The fuel rods are generally constructed from elongated cylindrical metal tubes containing nuclear fuel pellets and having both ends sealed by end plugs. These fuel assemblies are arranged in a vertically disposed lattice held together by intermittantly spaced positioning grids to form the reactor core. Typical reactor cores of this type are described and illustrated in U.S. Pat. No. 4,381,284. Although the fuel rods are designed to withstand the effects of the reactor operating environment, including those due to coolant hydraulics, reactor temperature and pressure, fission gas pressure, fuel expansion, and irradiation growth, defects in the fuel rods can often occur which could permit the escape of radioactive fission products.
As part of the continuing process of nuclear fuel development, it is therefore desirable and often necessary to conduct on-site visual examination of spent fuel assemblies for such defects as cracks, reduction of thickness, deformation, impression and corrosion, crud, bows and bulges, and changes in length, so that corrective action, for example, replacement and/or repair of defective or failed fuel rods may be undertaken and design changes may be employed in future fuel rod construction. The spent fuel assemblies are generally maintained underwater at a depth of about 40 to 45 feet, for cooling and shielding purposes, during removal from a reactor core and stored upright in a rack positioned within a spent fuel pool.
One of the many types of examinations required of the fuel assembly is a high magnification visual inspection of the peripheral fuel rods. On one hand, locating and inspecting a fuel rod within a fuel assembly is extremely difficult since such an assembly is radioactive and may contain hundreds of closely spaced fuel rods and guide thimbles. On the other hand, the assemblying and reassemblying of these fuel assemblies is time consuming and may, in itself, result in fuel rod damages. In addition, the area of the fuel rods subject to such damage as fretting is generally hidden by the grid of the fuel assembly. Thsu, only that side of the fuel rod facing the outside of the fuel assembly is accessible for visual inspection.
Thus, it can be appreciated that it is important to have a reliable system for manipulating radioactive fuel rods within a nuclear fuel assembly to permit the high magnification visual inspection of the peripheral fuel rods from a remote location without the need of at least the partial disassemblying of the fuel assembly, as well as permitting the visual inspection of such fuel rods arranged in a closely spaced array for inspecting and locating hidden defects by manipulation of the peripheral fuel rods.